In the case of data communication between so-called DTE equipment (Data Terminal Equipment)--such as PCs (Personal Computers), other forms of computers or like appliances--so--called TAE equipment (Terminal Adapter Equipment) is normally used to suitably adapt the digital representation of the DTE equipment to the communication network or networks used in the communication. Examples of communication networks that can be involved in such data communication are PSTN networks (Public Switched Telephone Networks, that is to say a typical telephone network), digital PLMN networks (Public Land Mobile Networks, that is to say a mobile telephone network) and an ISDN network (Integrated Services Digital Network).
TAE equipment used in communication with a PSTN network is normally referred to as a modem (abbreviation of modulator/demodulator). The modem modulates digital signals from the DTE equipment, so as to enable the signals to be transmitted via the PSTN network, and demodulates signals from the PSTN network to digital signals that can be understood by the DTE equipment.
TAE equipment used with an ISDN network is normally referred to as an ISDN adapter. An ISDN adapter converts between protocols that are used by the DTE equipment to protocols that are used over an ISDN network. Examples of such protocols are V.110 and X.25, which are specified by ITU.
TAE equipment used in communication with a PLMN network is normally referred to as a mobile telephone modem. The mobile telephone modem is not strictly a modem from a technical aspect, but rather a data converter that is connected between the DTE equipment and a mobile telephone. However, the mobile telephone modem fulfils the same functions as a modem in respect of DTE equipment, and enables the functions of the PLMN network to be utilized when coupled to the mobile telephone. A mobile telephone modem for the GSM system (Global System for Mobile communication) is also referred to as a GSM modem or GSM Data Card.
Co-operation between DTE equipment and TAE equipment is normally controlled by so-called AT-commands (AT is an abbreviated form of attention) transmitted between the DTE equipment and the TAE equipment. For instance, the DTE equipment can order calling, pausing, waiting for a ringing signal, and so on. In turn, the TAE-equipment can utilize the AT-commands to inform the DTE-equipment that it is engaged, that data transmission has been terminated, that no ringing tone has been obtained, and so on. The AT-commands were first introduced by the modem company Hayes and are today generally used with all modems and mobile telephone modems. However, other communication protocols that have a function corresponding to the function of the AT-commands also exist.
A given data bearer service specifies the parameters that shall be used in respect of data communication. These parameters may be, for instance, data rate, the number of start and stop bits, indication as to whether a synchronous or asynchronous communications mode shall be used, and an indication as to whether error correction shall be used over the communications link. For instance, there is found in the GSM system a number of ETSI-specified methods of arranging data communication. A special error correction protocol--RLP (Radio Link Protocol)--can be used. The RLP service is often referred to as a non-transparent service, whereas when RLP is not used, the service is consequently referred to as a transparent service. Start and stop bits can be used for each data packet. It is also possible to utilize the fact that the datastream in the GSM system is synchronous, thereby obviating the need to use start and stop bits. This enables the effective data rate to be increased. It is also possible to specify the actual data rate. Speeds of 2400, 4800 and 9600 bps can be used at present time, although data rate will be increased in the future. For instance, the data rate will be increased in the GSM system eight-fold, and will, of course, be increased still further in future broadband systems.
Not all data bearer services are supported by all PLMN networks. This is a drawback to the user. It is true that the data bearer service to be used can be set-up with the aid of the AT-commands, although in order for this to be achieved it is necessary for the user to be aware of :
Those data bearer services that are supported by the PLMN network. PA1 Those data bearer services that are most beneficial to the user. PA1 And how the AT-commands shall be used.
However, the normal user is not normally aware of these requirements. In order to circumvent this drawback, the mobile telephone modem is therefore default set to a data bearer service that is supported by all PLMN networks of the kind for which the modem is intended. Such is the case, for instance, with the GSM modem ERICSSON DC23, where one asynchronous and transparent data bearer service is default. The use of a default setting of the data bearer service means, of course, that the user will not normally obtain access to the data bearer service that is most beneficial to the user.